A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and S.R. Oates (U.Birmingham) for the Swift team
At 23:07:31 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 201216C (trigger=1013243) (Beardmore et al. GCN Circ. 29061). Swift did not slew immediately to the burst due to an observing constraint. At the time of the trigger, the initial BAT position was 116° from the Sun (7.4 hours East) and 86° from the 7%-illuminated Moon. Table 1 contains the best reported positions from Swift, and the latest XRT position can be viewed at http://www.swift.ac.uk/xrt_positions.
Izzo et al. (GCN Circ. 29066) reported the position from VLT for the optical afterglow of this GRB. Vielfaure et al. (GCN Circ. 29077) determined a redshift of 1.10 from VLT. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.
Standard analysis products for this burst are available at https://gcn.gsfc.nasa.gov/swift_gnd_ana.html.
As reported by Ukwatta et al. (GCN Circ. 29080),
the BAT ground-calculated position is RA, Dec = 16.364, 16.538 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows a multi-peaked structure that starts at ~ T-16 s and ends at ~T+64 s.
The main peak occurs at ~T+20 s.
The time-averaged spectrum from T-15.89 to T+64.11 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.43 ± 0.03.
The fluence in the 15-150 keV band is 4.5 ± 0.1 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1013243/BA/.
Analysis of the initial XRT data was reported by Evans et al. (GCN Circ. 29278). We have analysed 11 ks of XRT data for GRB 201216C, from 3.0 ks to 2506.3 ks after the BAT trigger. The data comprise 466 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 29067).
The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=1.97 (+0.10, -0.09).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.35 (+0.17, -0.16). The best-fitting absorption column is 7.7 (+1.2, -1.1) x 1
A summary of the PC-mode spectrum is thus:
Total column: 5.6 (+1.0, -0.9) x 1
Galactic foreground: 5.0 x 1
Excess significance: 9.3 σ
Photon index: 2.03 (+0.16, -0.15)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01013243.
The Swift/UVOT began settled observations of the field of GRB 201216C 2970 s after the BAT trigger
(Oates and Beardmore GCN Circ. 29071).
No optical afterglow consistent with the enhanced XRT position (Osborne et al. GCN Circ. 29067) or the VLT position (Izzo et al., GCN Circ. 29066) is detected in the initial UVOT exposures.
Table 3 gives preliminary
magnitudes using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc., 1358, 373).
No correction has been made for the expected extinction in the Milky Way
corresponding to a reddening of
Figure 1. The BAT
mask-weighted light curve in the four individual and total
energy bands. The units are counts
Figure 2. The XRT light curve.
Any data from a crosshatched region are not included in the fit.
RA (J2000) | Dec (J2000) | Error | Note | Reference |
---|---|---|---|---|
0 |
+16°30'58.0" | 1.4" | XRT-final | UKSSDC |
0 |
+16°30'58.0" | 1.6" | XRT-enhanced | Osborne et al. GCN Circ. 29067 |
0 |
+16°32'16.4" | 1.0' | BAT-refined | Ukwatta et al. GCN Circ. 29080 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Izzo et al. | 29066 | VLT afterglow candidate discovery | VLT | detection |
Optical | Jelinek et al. | 29070 | FRAM-ORM afterglow confirmation | FRAM | detection |
Optical | Vielfaure et al. | 29077 | VLT X-shooter spectroscopy and potential high redshift of a VHE-emitting GRB |
VLT | spectroscopy |
Optical | Shrestha et al. | 29085 | Liverpool Telescope First Hour Observations |
Liverpool Telescope | light curve |
Optical | Belkin et al. | 29210 | TSHAO, Terskol, Mondy optical upper limits |
Mondy | upper limits |
Optical | Gokuldass et al. | 29674 | VIRT optical observations | Virgin Island Robotic Telescope | |
Gamma-ray | Fermi | 29063 | Fermi GBM Final Real-time Localization | Fermi GBM | |
Gamma-ray | Malacaria et al. | 29073 | Fermi GBM detection | Fermi GBM | Fluence=1.41±0.06x1 (98.6 percentile for long GRBs) |
Gamma-ray | Nadella et al. | 29074 | AstroSat CZTI detection | CZTI | |
Gamma-ray | Blanch et al. | 29075 | MAGIC detection in very high energy gamma rays |
MAGIC | |
Gamma-ray | Bissaldi et al. | 29076 | Fermi-LAT upper limit | Fermi LAT | |
Gamma-ray | Frederiks et al. | 29084 | Konus-Wind detection | Konus-Wind | |
Gamma-ray | 2.at 2.UTC and Fermi-GBM | 29086 | No significant detection in HAWC | HAWC |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
2970 | 3120 | 147 | >20.0 |
white | 2970 | 3739 | 344 | >20.7 |
v | 3950 | 4150 | 197 | >19.1 |
b | 3334 | 3534 | 197 | >19.9 |
u | 3129 | 3329 | 197 | >19.3 |
m2 | 4154 | 4331 | 174 | >19.3 |
w2 | 3745 | 3945 | 197 | >19.7 |
Table 3. UVOT observations reported by Oates and Beardmore (GCN Circ. 29071). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.
March 20, 2021